How is the expected score for the second nine calculated for a 9-hole round?

The expected score on the second nine for a 9-hole round is necessary to calculate the 18-hole Score Differential for that round. The method for calculating the Score Differential is outlined in Rule 5.1 of the Rules of Handicapping. Unfortunately, neither the R&A nor the USGA publishes a formula for calculating the expected score.

Those interested in such calculations can: